Many consumer products are applied to the skin or hair, and/or involve the sensory experience of touching. Consumer preferences are influenced by a multitude of factors, including product effectiveness, the feel of the product, fragrance, durability, ease of rinsing, etc. One way to determine consumer preferences is by conducting consumer marketing tests, in which a representative group of consumers, or panelists, provide feedback after using a product. Consumer marketing tests have several drawbacks, however. Because panelists must be appropriately selected and compensated for their time, such tests are expensive and time consuming. Human feedback is inherently subjective, and may raise concerns about reliability. Products must be safe for human testing, and the analyses that can be performed after application also are limited.
Some product testing can be performed using model systems. Artificial substrates are available that, to some extent, imitate human skin. For example, theatrical performers often transform their appearance by using molded body parts that can be made to look remarkably like human skin. Alternatively, keratinous tissue from animals or human cadavers may be used. Whereas these and other available models may be suitable for some types of product testing, all have significant limitations. Cadaver tissue is costly, and neither cadaver nor animal tissue can truly mimic living, human tissue. Previously available artificial substrates provide poor models to assess characteristics such as product adsorption, rinseability, and the look and feel of a product upon application.
In a previous application, applicants addressed some shortcomings of available models by applying to a suitable substrate one or more coating materials which allow variation of surface energy, surface charge and surface reactivity. In this manner, a surface can be created which mimics various types of keratinous tissue, for example, wet, dry, young, aged skin etc. on various parts of the body. A challenge remained, however, to create a model which, in addition to the aforementioned properties, mimics the elasticity, compressibility and appearance of skin. For example, when skin is stroked or rubbed, a given amount of stretching and movement of the skin occurs. When pressure is applied to skin, some compression occurs. If the skin has sufficient elasticity, it may resume its original form when the rubbing and/or pressure are ceased. Furthermore, the natural appearance of skin, including tone and pigmentation, is due in part to its various layers. For example, the outermost layer of skin, the stratum corneum, typically is more transparent than the underlying dermal layer, which contains skin pigments. The interactions of light with the various layers, such as refraction and/or reflection of pigmentation by the stratum corneum, along with localized differences in coloration, result in the skin's natural appearance.
In addition, skin elasticity, compressibility, appearance and other characteristics change over time and may vary widely, depending upon factors such as the type of skin, the time of day, amount of sleep, the location on the body, age, environmental conditions, diet, gender, and disease, to name a few. For example, skin elasticity tends to decrease with age. Compressibility may increase with disease states such as edema or with an increase in underlying fatty tissue. Currently available models fail to adequately mimic skin compressibility and elasticity, may exhibit undesirable characteristics such as “bleeding” (a leaking of underlying material to the surface) or stickiness, and furthermore tend to have a uniform color and mask-like appearance. There exists a need, therefore, to provide an artificial substrate that more accurately mimics the elasticity, compressibility, appearance and other relevant physical properties of a variety of skin types.